Bluetooth: Mesh: Fix set friend_cred flag incorrectly
Bluetooth: Mesh: Fix set friend_cred flag incorrectly

Only set friend_cred to true when friendship established and
use friend cred security material decryption successfully.

Signed-off-by: Lingao Meng <8f6064192f8620c0146f45d3572dde5f622ecf12@gmail.com>

nashif/zephyr,Vudentz/zephyr,galak/zephyr,finikorg/zephyr,Vudentz/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,nashif/zephyr,galak/zephyr,finikorg/zephyr,galak/zephyr,galak/zephyr,nashif/zephyr,Vudentz/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,finikorg/zephyr,nashif/zephyr,Vudentz/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr